Sexual recruitment of trees following fire in the southern mixedwood boreal forest of Canada

Abstract

The establishment following fire of four tree species, Pinus banksiana Lamb., Picea mariana (L.) Mill., Picea glauca (Moench) Voss and Populus tremuloides Michx., was studied in the mixedwood boreal forest of Saskatchewan, Canada. The main objective of the study was to estimate the recruitment densities of germinants as a function of seedbed type. Field observations indicate that there are significant differences in seedbed frequencies between sites. The study also demonstrates that all species establish preferentially around tree boles where there is exposed mineral soil and humus. While there is no significant difference between germinant densities on mineral soil and humus, there are, on average two times more germinants on those seedbeds than on organic layer (O$\rm\sb{f}$) seedbeds. In addition, there is evidence for an inverse relationship between germinant survival and organic layer thickness. There is also evidence that moisture in the major factor controlling germinant survival in the field. The study shows that a sequence of stage-specific survival values can be used to accurately estimate recruitment densities. Finally, it demonstrates that there are essentially only three cohorts following a fire; that germinant mortality declines with time; and that survival subsequently approaches one and becomes independent of seedbed type. The result of the study now give investigators a standard for comparison with post-clearcut recruitment densities.